Many kinds of removable band-type couplings for pipes exist in the art. It is noted that throughout the specification and claims, the term “pipe” encompasses any kind of generally cylindrical object.
In general, pipe couplings have an elastomeric seal member, and when the coupling is tightened, the seal member seals against the outer contour of two pipes inserted in the coupling. Due to hydraulic forces caused by liquid flowing in the pipes, as well as other factors, the pipe coupling is subject to axial forces that tend to make the coupling shift axially along the pipes. Accordingly, manufacturers have developed different axial-restraint pipe couplings, which have different mechanisms for counteracting the axial forces on the coupling.
For example, U.S. Pat. No. 7,571,940 to Krausz describes a pipe coupling that combines an elastomeric seal member with a grip ring. The grip ring is formed of wedge-shaped grip elements that are radially spaced from one another about a ring member, such as springs that connect adjacent grip rings with one another. The grip elements are formed with teeth that face inwards towards the center of the ring. A single fastener (e.g., bolt and nut or other tightenable screw) is provided, which when tightened in a direction transverse to the axial length of the pipe, presses both the elastomeric seal member and the grip ring against the surface of the pipe. The teeth of the grip ring act against the axial forces.
U.S. Pat. No. 6,851,728 describes a pipe coupling with an externally-threaded joint body, a locknut, an annular core member disposed within the locknut, and a plurality of locking members retained in apertures of the core member to be spaced circumferentially apart from each other. Upon tightening rotation of the locknut around the joint body, the internal conical surface of the locknut slidably contacts with the conical surfaces of the locking members so as to press the locking members radially inwardly, to cause the gripping portions of the locking members come into gripping engagement with the outer periphery of the inserted pipe, to act against axial forces.